Adjusting device of belt tension

ABSTRACT

A belt tension adjusting device composed to ease positive detection of plastic elongation of belt is proposed. The time for the belt to be replaced by new one can be recognized in early stages and accurately. The plastic elongation of the belt can be detected visually from the front or upper side of an engine without unsighted by the auto-tensioner (automatic belt tension adjuster) and the belt. Further, workability of replacing belt is improved.  
     The device comprises a crank pulley ( 1 ), accessory drive pulleys, a belt looped over the pulleys, a tension pulley ( 5 ), an actuator ( 32 ), a connecting arm ( 8 ), an auto-tensioner ( 3 ) for adjusting belt tension automatically, an indicating member which is attached to the moving end of the actuator ( 32 ) to move in conjunction with the moving end, and an detecting member for detecting the position of the indicating member, whereby the plastic elongation of belt can be estimated by detecting the position of the indicating member visually.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a belt tension adjusting device to beapplied to an engine mounted on a vehicle, etc., the device comprisingan accessory drive pulley connected to a crank pulley of an engine bymeans of a belt, a tension pulley for adjusting the tension of the belt,and an auto-tensioner (automatic belt tension adjuster) for adjustingbelt tension by changing the position of rotation center of the tensionpulley by means of an actuator.

2. Description of the Related Art

As for belt transmission for driving accessories of an engine, belttension adjusting devices are disclosed for example in JP11-82652A,JP11-8100851A, JP2002-323101A and JP2003-27953A. The device having atension pulley for adjusting the tension of the belt and anauto-tensioner (automatic belt tension adjuster) which is composed suchthat the position of rotation center of the tension pulley is moved byshifting the moving end of an actuator, the moving end being connectedto the tension pulley by means of a connecting arm. According to thesebelt tension adjusting devices, belt tension is automatically adjusted,but how much the center of the tension pulley is moved for adjusting thetension of the belt can not be detected.

In FIGS. 10˜12 is shown an example of belt tension adjusting device ofprior art for bus engine, which comprises a tension pulley andauto-tensioner, and with which the amount of shift of the center of thetension pulley can be detected. FIG. 10 is a side view along thecrankshaft center line, FIG. 11 is an elevation viewed in the directionof the crankshaft center line, and FIG. 12 is an elevational view of thetension pulley and auto-tensioner.

In the drawings, reference numeral 105 is an engine, 100 is a radiator,102 is a radiator fan, 101 is a shroud covering said radiator fan 102,103 is an alternator, 104 is a compressor for an air conditioner, and106 is the crankshaft center line of the engine 105.

Reference numeral 1 is a crank pulley fixed to the crankshaft of saidengine 105, 107 is an air conditioner pulley fixed to the rotation shaftof said compressor 104 for air conditioner, 4 is an alternator pulleyfixed to the rotation shaft of said alternator 103, and 108 is a waterpump pulley fixed to the rotation shaft of a water pump (not shown inthe drawings).

Reference numeral 5 is a tension pulley. Reference numeral 2 is a beltlooped over said crank pulley 1, water pump pulley 108, air conditionerpulley 107, alternator pulley 4, and tension pulley 5. Torque istransmitted from said crank pulley 1 to said water pump pulley 108, airconditioner pulley 107, and alternator pulley 4 by means of said belt 2to drive accessories such as said water pump (not shown in thedrawings), compressor 104 for air conditioner, alternator 103, etc.

Reference numeral 3 is an auto-tensiner (automatic belt tensionadjuster) for adjusting the tension of said belt 2. Reference numeral 15is a supporting shaft to support said auto-tensioner, 32 is an actuator,7 is an auto-tensiner connecting shaft connected to the moving end ofsaid actuator 32, and 8 is a connecting arm for connecting theauto-tensioner connecting shaft 7 at the moving end of the actuator 32to a tension pulley supporting shaft 13 supporting said tension pulley 5for rotation. The connecting arm 8 is supported for rocking by asupporting shaft 6 attached to said engine 105.

The tension of said belt 2 can be adjusted by moving the moving end ofthe actuator 32 of said auto-tensioner 3. When the auto-tensionerconnecting shaft 7 connected to the moving end of the actuator 32 of theauto-tensioner 3 is shifted by operating the actuator 32, the connectingarm 8 is turned around the center of the supporting shaft 6, whereby theposition of the tension pulley supporting shaft 13 and the tensionpulley 5 supported by the tension pulley supporting shaft 13 is changedto allow the tension of the belt 2 to be adjusted.

Reference numeral 110 is a pointer fixed to the connecting arm 8, and111 is a scale plate fixed to the engine 105. As the pointer 110 turnstogether with the connecting arm and the scale plate is fixed to theengine, how much the connecting arm 8 is turned relative to the enginecan be visually detected by means of the pointer 110 and scale plate111. Thus, the travel of the center of said tension pulley 5, which is abarometer to show how much the belt elongated plastically, can bevisually detected. According to this prior art, the pointer 110 attachedto the connecting arm 8 protrudes from the arm and the rotated angle ofthe connecting arm is detected by finding the position of the tip of thepointer 100 which vibrates relatively violently due to engine vibration,and the tip of the pointer 110 and the scale plate 111 is positionedwhere it is not easy to inspect visually due to the presence of theactuator 32 as shown in FIG. 11.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a belt tensionadjusting device for an engine, with which plastic elongation of beltcan be detected positively and accordingly the time for the belt to bereplaced by new one is detected accurately in early stages, and withwhich plastic elongation of belt can be detected visually easily fromthe upper side or front side of the engine without unsighted by theauto-tensioner (automatic belt tension adjuster) and/or the belt.

To attain the object mentioned above, the present invention proposes abelt tension adjusting device comprising: a crank pulley; an accessorypulley or pulleys; a belt looped over said pulleys to transmit thetorque of said crank pulley to said accessory pulley or pulleys fordriving an accessory or accessories; a tension pulley pushing the beltto give tension to the belt; an auto-tensioner (automatic belt tensionadjuster) for adjusting belt tension automatically, the auto-tensionercomprising an actuator and a connecting arm, a fixing end of saidactuator being supported by a supporting shaft attached to the body ofthe engine, a moving end of said actuator being connected to an end partof said connecting arm, the tension pulley being supported for rotationat the other end part of the connecting arm, the connecting arm beingsupported for rocking by a supporting shaft attached to the body of theengine at an intermediate position between both ends of the connectingarm so that the rotation center of said tension pulley being able to beshifted by the travel of the moving end of said actuator to adjust belttension; an indicating member attached to the moving end of saidactuator so that the indicating member moves in conjunction with saidmoving end; a detecting member for finding the position of saidindicating member; whereby the state of stretch of the belt (i.e. theplastic elongation of the belt) is judged through detecting the positionof said indicating member by said detecting member.

According to the invention, the device is composed such that the stateof stretch of the belt (plastic elongation of the belt) is judged bydetecting the position of the indicating member which moves as plasticelongation of belt increases because belt tension is adjustedautomatically. Therefore, plastic elongation of belt can be estimatedrelatively accurately by detecting the amount of the shift of the movingend of the actuator, and the time for the belt to be replaced can bejudged accurately in early stages. (Of course, the amount of the shiftof the moving end of the actuator is influenced not only by the plasticelongation of the belt, but by the wear of the pulleys and belt,direction of the shift of the tension pulley, and spring force of theactuator which varies as the amount of the shift varies. However, theelastic elongation can be estimated relatively accurately by the amountof the shift of the moving end of the actuator.)

In the invention, it is preferable that said indicating member is abar-like member extending in the direction of the axis of said actuatorwith an end thereof connected to the moving end of said actuator, theprotrusion length of the other end of the indicating member protrudingfrom said detecting member is detected, whereby it is judged that theplastic elongation of the belt has reached the maximum permissible valuewhen said protrusion length has reached the maximum permissible length.

With this composition, as the plastic elongation of the belt can beestimated by detecting the protruding length of the bar-like indicationmember located along the side of the auto-tensioner, the amount of shiftof the moving end of the actuator can be detected visually from thefront side of the engine without unsighted by the auto-tensioner and/orthe belt.

The plastic elongation of the belt can be estimated from the amount ofshift of the moving end of the actuator, accordingly from the positionof the indicating member. Thus, the plastic elongation is easily andaccurately judged visually by means of the bar-like member.

It is also preferable that said detecting member is a scale or gradationmarks provided in the vicinity of the moving end of said actuator sothat the amount of shift of said indication member can be detected.

By composing like this, the amount of shift of the moving end of theactuator can be perceived visually and easily without unsighted by theactuator.

It is also preferable that a belt life limit range is indicated on saiddetecting member to indicate the permissible limit of plastic elongationof belt. By this, the time for the belt to be replaced can be easilyjudged by visual inspection only by detecting that the position of saidindicating member comes in said belt life limit range.

It is also preferable that said indicating member is a bar-like memberextending in the direction of the axis of said actuator with an endthereof connected to the moving end of said actuator and with the otherend part provided with an indicating part, said detecting member is ascale member attached to the fixing end of said actuator and hasgraduation marks formed thereon to detect the position of saidindicating part.

With this composition, the plastic elongation of the belt can bedetected by means of said indication member located near the top of thebar-like member which moves in conjunction with the moving end of theactuator and the scale member attached to the fixing end located at theupper part of the actuator, so that the plastic elongation of the beltcan be detected visually easily from the upper side of the enginewithout unsighted by the auto-tensioner and/or the belt.

It is also preferable that said indicating member is an indicating partprovided on the moving end of said actuator and said detecting member isa scale member attached to said connecting arm to detect the position ofsaid indicating part.

With this composition, as the indicating part and scale member arelocated at the actuator's moving end side which faces to the front sideof the engine, the indication part and scale are viewable from the frontside of the engine, and as the scale member is attached on the surfaceof the connecting arm, the scale member can be attached with ease.

Further, as said indicating member is attached to the moving end of theactuator, the amount of shift of the indicating member is large andvisibility is good.

It is preferable that said indicating member and detecting member arelocated in a position near to an inspection door provided in a rear partof the floor of a rear engine bus. By this, the indicating part andscale can be easily inspected visually through the inspection doorprovided on the floor in the rear part of the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of the first embodiment of the belttension adjusting device of an engine for a bus according to the presentinvention.

FIG. 2 is a sectional side view of the auto-tensioner.

FIG. 3 is a partial elavational view of the second embodiment of thedevice showing the tension pulley and auto-tensioner.

FIG. 4 is a view of the third embodiment corresponding to FIG. 3.

FIG. 5 is a view of the fourth embodiment corresponding to FIG. 3.

FIG. 6 is a view of the fifth embodiment corresponding to FIG. 3.

FIG. 7(A) is a view of the sixth embodiment corresponding to FIG. 3, andFIG. 7(B) is a sectional view showing the state the stopper is inserted.

FIG. 8 is a view of the seventh embodiment corresponding to FIG. 3.

FIG. 9 is a view of the eighth embodiment corresponding to FIG. 3.

FIG. 10 is a side view of an example of belt tension adjusting device ofprior art.

FIG. 11 is an elevational view of the device shown in FIG. 10.

FIG. 12 is an elevational view of the tension pulley and auto-tensionerof the device shown in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1˜FIG. 8 showing the first to seventh embodiment, theconfiguration and arrangement of an engine 105, radiator 100, radiatorfan 102, shroud 101 for covering the radiator, alternator 103,compressor 104 for an air conditioner, crank pulley 1 fixed to thecrankshaft of said engine 105, air conditioner pulley 107 fixed to therotation shaft of said compressor 104 for air conditioner, alternatorpulley 4 fixed to the rotation shaft of said alternator 103, water pumppulley 108 fixed to the rotation shaft of a water pump (not shown in thedrawings), tension pulley 5, etc. and the configuration and arrangementof a belt 2 looped over said crank pulley 1, water pump pulley 108, airconditioner pulley 107, alternator pulley 4, and tension pulley 5 aresimilar to the prior art shown in FIGS. 10 and 11.

In FIG. 1 and FIG. 2 showing the first embodiment, reference numeral 1is a crank pulley, 4 is an alternator pulley, 2 is a belt looped oversaid crank pulley 1, water pump pulley 108 (see FIG. 11), airconditioner pulley 107 (see FIG. 11), alternator pulley 4, and tensionpulley 5. Torque is transmitted from said crank pulley 1 to said waterpump pulley 108, air conditioner pulley 107, and alternator pulley 4 bymeans of said belt 2 to drive accessories such as said water pump (notshown in the drawings), compressor 104 for air conditioner (see FIG.10), alternator 103 (see FIG. 10), etc. Reference numeral 106 is thecrankshaft center line of the engine 105.

Reference numeral 3 is an auto-tentioner (automatic belt tensionadjuster) for adjusting the tension of the belt 2, 32 is an actuator ofthe auto-tensioner 3. Reference numeral 15 is an auto-tensionersupporting shaft to support the fixing end of the actuator 32, saidauto-tensionar 3 being fixed to the body part 11 of said engine (seeFIG. 11) by the supporting shaft 15. Reference numeral 7 is anauto-tensioner connecting shaft attached to the moving end of saidactuator 32. Reference numeral 13 is a tension pulley supporting shaftwhich supports said tension pulley 5 for rotation.

Reference numeral 8 is a connecting arm, which is supported by asupporting shaft 6 attached to the body part 11 of the engine at acenter part thereof to be capable of rocking motion and which supportssaid auto-tensioner connecting shaft 7 at an end thereof and saidtension pulley supporting shaft 13 at the other end thereof so that themovement of the moving end of said actuator 32 is transmitted to changethe center position of said tension pulley 5.

When the belt 2 elongates plastically, which induces a reduction in belttension, the moving end of the actuator 3 and accordingly theauto-tensioner connecting shaft 7 is shifted by the spring force of aspring 31 in the auto-tensioner 3 by a length corresponding to thereduction in the belt tension. Said connecting arm 8 is turned aroundthe center of the supporting shaft 6 by the shift of the auto-tensionerconnecting shaft 7, and said tension pulley supporting shaft 13 andaccordingly the tension pulley 5 supported by the tension pulleysupporting shaft 13 is shifted to adjust the tension of the belt 2. Inthis way, the tension of the belt 2 is corrected automatically.

Reference numeral 10 is a guide rod which serves as a pointer member forindicating the travel of the auto-tensioner connecting shaft 7 attachedto the moving end of the actuator 32. The guide rod 10 is disposedoutside the actuator 32 along the axial direction thereof with an end ofthe rod connected to an end of the auto-tensioner connecting shaft 7 asshown in FIG. 2 so that the rod 10 is moved in conjunction with themovement of the moving end of the actuator 32. The guide rod 10 islocated outside the auto-tensioner 3 at a position near toward the upperside of engine, and the other end side of the rod is fitted slidably toa bush 12 a fitted tightly to the body part 11 of the engine, the endface of the bush 12 a being a detecting member. Reference numeral 12 isa stopper attached to the top end part of the guide rod 10.

According to the first embodiment, when the moving end of the actuator32 of the auto-tensioner 3, accordingly the auto-tentioner connectingshaft 7 shifts due to a plastic elongation of the belt and the tensionpulley 5 supported by the tension pulley supporting shaft 13 is shiftedas mentioned above, the guide rod 10 connected to the auto-tensionerconnecting shaft 7 is moved in the direction indicated by arrow y inFIG. 2, and protruding length s of the guide rod protruding from the endface of the bush 12 a decreases.

When said protrusion length s decreases to zero and the stopper 12attached to the top end part of the guide rod 10 contacts the end faceof the bush 12 a, it is judged that the plastic elongation of the belt 2has reached the maximum limit and the belt 2 should be replaced by newone.

Therefore, according to the first embodiment, a change in protrudinglength s of the guide rod 10 from the end face of the bush 12 a(detecting member) located outside the auto-tensioner 3 at a positionnear toward the upper side of engine, that is, a change in protrudinglength from the engine body is detected and it is judged that theplastic elongation of the belt has reached the maximum limit, i.e. thetime for the belt to be replaced has reached when said protruding lengths becomes zero and the stopper 12 contacts the end face of the bush 12a, so that the travel of the moving end of the actuator 32, accordinglychanges in plastic elongation can be detected from the front side of theengine by observing the guide rod without unsighted by theauto-tensioner 3 and the belt 2.

As the belt tension adjusting device of the invention is composed suchthat the travel of the guide rod 10 connected to the auto-tensionerconnecting shaft 7 which is attached to the moving end of the actuator32 of the auto-tensioner 3 is detected by the protruding length s of theguide rod 10 to judge the stretched state of the belt 2, an increase inplastic elongation of the belt which induces a reduction in belt tensioncan be accurately detected, because the shift of the moving end of theactuator 32 in correspondence with the plastic elongation of the belt isrelatively large. Therefore, with this configuration, it is possible torecognize the stretched state of the belt 2 (plastic elongation of thebelt 2) and the time for the belt 2 to be replaced in early stages andaccurately.

Further, as the travel of the moving end of the actuator 32, accordinglythe stretched state of the belt and changes in plastic elongation of thebelt, can be detected from the front side of the engine withoutunsighted by the auto-tensioner 3 and belt 2 by means of the guide rod10, visibility and also accuracy of detecting changes in plasticelongation of the belt can be improved.

The second to seventh embodiments shown in FIGS. 3 to 8 are similar incomposition to the device of the first embodiment except that the guiderod 10 as an indicating member and the bush 12 a fixed to the enginebody as a detecting member are replaced by members as described in thefollowing.

In FIG. 3 showing the third embodiment, a pointer 22 which is anindicating member is fixed to the moving end of the actuator 32 near theauto-tensioner connecting shaft 7 and a scale plate 21 is provided tothe engine body 11, the pointer 22 and scale plate 21 being shaped to beeasy for visual observation, so that the travel of the pointer 22 can bedetermined by the scale plate 21.

According to the second embodiment, as the pointer 22 and the scaleplate 21 are located at the position where the travel of the moving endof the actuator 32 is large and visual evaluation thereof is easy, thevisual determinability of plastic elongation of the belt 2 is improvedand it becomes possible to predict the time for the belt to be replaced.

In FIG. 4 showing the third embodiment, the pointer 22 which is anindicating member is fixed to the moving end of the actuator 32 near theauto-tensioner connecting shaft 7 as is the case with the firstembodiment, and a scale plate 23 on which is marked a belt life limitrange 24 is provided to the engine body so that the travel of thepointer 22 can be determined by the scale plate 23.

According to the third embodiment, it is judged that the life of thebelt has expired when the pointer 22 reaches the belt life limit range,and the time for the belt 2 to be replaced can be judged visually easilyonly by detecting that the pointer 22 points to the belt life limitrange indicated on the scale plate 23.

In FIG. 5 showing the fourth embodiment, reference numeral 26 is abar-like indicating member extending along the axial direction of theactuator 32 with an end of the indicating member 26 fixed to the movingend of the actuator 32 near the auto-tensioner connecting shaft 7 sothat the indicating member 26 is movable together with the moving end ofthe actuator 32. A pointer 35 which is a pointing part is provided inthe top end part of the indicating member 26. Reference numeral 27 is asupporting member for supporting the intermediate portion of theindicating member 26 so that the member 26 can move in the axialdirection of the actuator 32.

Reference numeral 25 is a scale member fixed to the fixing end of theactuator 32 and having graduation marks formed thereon.

According to the fourth embodiment, the plastic elongation of the belt 2can be detected by means of the pointer 35 provided in the top end partof the bar-like indicating member 26 which moves in conjunction with themoving end of the actuator 32 and the scale member 25 attached to thefixing end provided at the upper part of the actuator 32, so the plasticelongation of the belt 2 can be detected, the visual determinability ofplastic elongation of the belt 2 is improved, and it becomes possible topredict the time for the belt to be replaced.

In FIG. 6 showing the fifth embodiment, reference numeral 42 is apointer which is an indicating part fixed to the moving end of theactuator 32, 41 is a scale member attached to the connecting arm 8 sothat the travel of the pointer 42 can be determined by the scale plate41.

According to the fifth embodiment, as the pointer 42 and the scalemember 41 are located at a position where the travel of the moving endof the actuator 32 is large, visibility is improved, and as the scalemember 41 is attached to the surface of the connecting arm 8, it is easyto attach the scale member 41.

In FIG. 7(A) showing the sixth embodiment, reference numeral 26 is abar-like indicating member extending along the axial direction of theactuator 32 with an end of the indicating member 26 fixed to the movingend of the actuator 32 near the auto-tensioner connecting shaft 7 sothat the indicating member 26 is movable together with the moving end ofthe actuator 32. In the top end part of the indicating member 26 isprovided a pointer (not shown in the drawing). Reference numeral 27 is asupporting member for supporting the intermediate portion of theindicating member 26 so that the member 26 can move in the axialdirection of the actuator 32.

Reference numeral 25 is a scale member fixed to the fixing end of theactuator 32 and having graduation marks formed thereon.

Reference numeral 44 is a stopper. The stopper 44 has a groove 44 a asshown in FIG. 7(B) and can be inserted between the top end surface ofthe fixing end 45 of the actuator 32 and the undersurface of the flange26 a formed at the top end of the indicating member 26, the indicatingmember 26 passing through the groove 44 a of the stopper 44 when it isinserted. By inserting the stopper, the moving end of the actuator ismoved upward and the tension pulley 5 is moved downward, whereby thebelt 2 is slackened.

According to the sixth embodiment, the actuator 32 is locked in acontracted state in which the moving end of the actuator is movedagainst the spring force of the spring 31 in the direction indicated byarrow Y by inserting the stopper 44 between the fixing end 45 of theactuator 32 and the flange 26 a of the indicating member 26. By lockingthe actuator 32 in the contracted state, the pushing force of thetension pulley 5 pushing the belt 2 is removed to relax the tension ofthe belt 2, and the belt 2 can be easily replaced by new one withoutnecessity of using any force to resist the belt tension because the beltis slackened, therefore workability of replacing belt is improved.

In FIG. 8 showing the seventh embodiment, the device is composed suchthat the actuator 32 can be locked in an extended state as against thecase of the sixth embodiment in which the actuator 32 is locked in acontracted state. Other than this, the seventh embodiment is composedthe same as the sixth embodiment shown in FIG. 7.

In FIG. 8, reference numeral 54 is a stopper used when locking theactuator in an extended state. The stopper 54 is attached to the fixingend of the actuator 32 by engaging a protrusion formed on an inner sideof the stopper 54 with a groove formed on a side of the fixing member ofthe actuator 32. The top part of the stopper 54 contacts the top surfaceof the flange 26 a formed at the top of the indicating member 26. Thisembodiment is applied when the belt is slackened by locking the actuatorin an extended state.

According to the seventh embodiment, the actuator 32 is locked in anextended state in which the moving end of the actuator is moved in thedirection indicated by arrow Y pushed by the spring force of the spring31 by attaching the stopper 54 so that the top part thereof contacts thetop surface of the indicating member 26. By locking the actuator 32 inthe extended state, the pushing force of the tension pulley 5 pushingthe belt 2 is removed to relax the tension of the belt 2, and the belt 2can be easily replaced by new one without necessity of using any forceto resist the belt tension because the belt is slackened, andworkability of replacing belt is improved.

In the eighth embodiment shown in FIG. 9, the belt tension adjustingdevice of the first to seventh embodiment is located in the rear part ofthe vehicle body, where an inspection door 115 is provided, of a rearengine bus. As the belt tension adjusting device of the first to seventhembodiment is composed so that the travel of the moving end of theactuator is perceived visually, the travel can be inspected easilythrough the inspection door 115.

In FIG. 9, reference numeral 1 is a crank pulley, 108 is a water pumppulley, 107 is an air conditioner pulley, 4 is an alternator pulley, 5is a tension pulley, and 2 is a belt looped over the pulleys.

1. A belt tension adjusting device for an engine comprising: a crankpulley, an accessory pulley or pulleys, a belt looped over said pulleysto transmit the torque of said crank pulley to said accessory pulley orpulleys for driving an accessory or accessories, a tension pulleypushing the belt to give tension thereto, an auto-tensioner (automaticbelt tension adjuster) for adjusting belt tension automatically, theauto-tensioner comprising an actuator and a connecting arm, a fixing endof said actuator being supported by a supporting shaft attached to thebody of the engine, a moving end of said actuator being connected to anend part of said connecting arm, the tension pulley being supported forrotation at the other end part of the connecting arm, the connecting armbeing supported for rocking by a supporting shaft attached to the bodyof the engine at an intermediate position between both ends of theconnecting arm so that the rotation center of said tension pulley beingable to be shifted by shifting the moving end of the actuator to adjustthe tension of the belt, an indicating member attached to the moving endof the actuator so that the indicating member moves in conjunction withsaid moving end, a detecting member for finding the position of saidindicating member; whereby the state of stretch of the belt (i.e. theplastic elongation of the belt) is judged through detecting the positionof said indicating member by said detecting member.
 2. The belt tensionadjusting device according to claim 1, wherein said indicating member isa bar-like member extending in the direction of the axis of saidactuator with an end thereof connected to the moving end of saidactuator, the protrusion length of the other end of the indicatingmember protruding from said detecting member is detected, whereby it isjudged that the plastic elongation of the belt has reached the maximumpermissible value when said protrusion length has reached the maximumpermissible length.
 3. The belt tension adjusting device according toclaim 1, wherein said indicating member is a bar-like member extendingin the direction of the axis of said actuator with an end thereofconnected to the moving end of said actuator and with the other end sideguided by said detecting member provided in the vicinity of the fixingend of said actuator, the protrusion length of the other end of thebar-like member protruding from said detecting member is detected,whereby it is judged that the plastic elongation of the belt has reachedthe maximum permissible value when said protrusion length has reachedthe maximum permissible length.
 4. The belt tension adjusting deviceaccording to claim 1, wherein said indicating member is a bar-likemember extending in the direction of the axis of said actuator with anend thereof connected to the moving end of said actuator and with theother end part provided with an indicating part, said detecting memberis a scale member attached to the fixing end of said actuator and hasgraduation marks formed thereon to detect the position of saidindicating part.
 5. The belt tension adjusting device according to claim1, wherein said detecting member is a scale or gradation marks providednear the moving end of said actuator for detecting the position of theindicating member provided to said moving end.
 6. The belt tensionadjusting device according to claim 1, wherein a belt life limit rangeis indicated on said detecting member to show the permissible limit ofplastic elongation of belt.
 7. The belt tension adjusting deviceaccording to claim 1, wherein said indicating member is an indicatingpart provided on the moving end of said actuator and said detectingmember is a scale member attached to said connecting arm to detect theposition of said indicating part.
 8. The belt tension adjusting deviceaccording to claim 1, wherein said indicating member and detectingmember are located in a position near to an inspection door provided ina rear part of the floor of a rear engine bus.
 9. The belt tensionadjusting device according to claim 2, wherein said indicating member isformed to have a flange part so that a stopper member can be insertedbetween said flange part and the fixing end of said actuator in order tomake it possible to replace easily the belt by new one by locking thetelescopic travel of said moving end and allowing the pushing force ofsaid tension pulley pushing the belt to be released.